union is really a mechanical one. It is a union of cells, and in that
respect it is simply mechanical, not a physiological union. The
different life types or character of the scion and top do not fuse, but
we have a mechanical union of cells, and that mechanical union is as
clearly shown forth as possible when we make a section through the point
of union. If your type of cell in the stock differs very materially from
the type of structure in the scion, the union is unsatisfactory. If the
types of tissue are much alike, the union is good and you do not have
either overgrowth of stock or undergrowth of scion very much, but you
have what is called a good union. It is to some extent a question of
mechanics, in my judgment, influenced by the cell structure of stock and
scion. If you have a good, smooth union, the two grow equally. Where you
have overgrowth of scion, you usually have a starved root, because the
food which is to be returned elaborated is checked at the point of
union, the root is starved, and you have a short lived tree, because
your root system, which ought to receive its share of the distributed
food, is underfed, finally weakens, and the whole structure fails.
Professor Lake: You may have mechanical union, but you can't have the
after fusion in which you are going to have proper function of stock and
scion.
Professor Craig: Each cell functions after its own kind. It is a
question of passage or transmission of food through that carrier, after
the union is effected. If the character of the two types differs very
much, the transmission of food is checked and is difficult.
President Morris: There is another mechanical point I'd like to ask
about. When the two types of cells differ, will the difference in degree
of capillarity regulate the amount of pabulum distributed, or does it
depend upon negative and positive pressure?
Professor Craig: That is a very difficult question, because it isn't
settled at the present time what credit we should give to capillarity
and what to root pressure in sap circulation.
Mr. Reed: There is another question I would like to ask Professor Craig.
Supposing you have a mechanical union perfected, what is the difference
in the food that different species of the same genus transmit? Has that
been worked out?
Professor Craig: I don't think so. Of course, there is a difference in
the food. That is proven, because there is a difference in the quality
of the food. The tree machine, the tree factory speaking individually,
evidently makes different products, and that is shown by the different
quality of nuts. That is all we know about it.
Professor Lake: That part below the scion still continues to be normal
hickory, and that part above, pecan, so really it is not a matter of
distribution of water supply by gravity or other pressure, but rather a
distribution of the proper amount of elaborated food; and that is
transmitted through the cell itself, not the cell walls. Because this
top makes a food that is different from the normal requirements, or
because the latent character of those cells below does not respond to
the food supply as actively as the part above, is the whole question, it
seems to me. If the cells below functioned as the cells above, there
would be no question about the stock and scion being the same.
Mr. Littlepage: Of course there must be sufficient flow of sap to
distribute food. The hickory root might not send the flow of sap as fast
as the pecan top would like.
Mr. Reed: Is Mr. Lake's point always true, that the stock below the
point of union remains a normal hickory?
Professor Craig: I don't believe there are more than one or two
exceptions noted to that, and those exceptions are recorded under graft
hybrids.
Mr. Reed: A seedling pecan tree owned by Mr. B. M. Young of Morgan City,
Louisiana, was top worked with scions from the McAllister hican some
seven or eight feet above ground, and later on the bark of the pecan
trunk below the point of union became scaly like that of the hican
above.
Professor Lake: That would suggest something worth while, if that part
below would produce fruit like the part above, but I would want to
question a little the modification in bark characteristics being a
direct result of cross grafting.
Mr. Reed: Of course, it was no check--only one instance.
Professor Craig: There are one or two others that are authentic. I have
known a case of plum. Here we have the plum stock, we will say it is
_Prunus Americana_, grafted with _Prunus triflora_, the Japanese, then
later on, _Prunus domestica_ is put on top. I have seen a sprout from
triflora bearing Japanese plums, while the top of the tree bore _Prunus
domestica_, although there was only a small section of stem in there
between our two distinct species. They were perfectly normal.
President Morris: Each elaborates its own kind of food in its own kind
of cell. I would like to hear from Mr. Brown and Mr. Wilcox on this
matter of grafting--the influence of stock on scion.
Mr. Wilcox: We had a good show of stocks, but instead of allowing them
to become established in the pots, we grafted them as they started into
growth after rooting. Had they been established, we would have expected
better results.
Professor Craig: What method do you employ?
Mr. Wilcox: Side grafting.
Professor Craig: Do you mean whip grafting?
Mr. Wilcox: Side whip grafting.
Doctor Deming: I would like to ask Doctor Morris what he thinks of the
practical future of grafting our hickory seedlings with improved
varieties of hickory or pecan, and the method most likely to
succeed,--whether grafting or budding, and at what season. It is
important to learn whether we can so graft or bud our hickory sprouts
that within a few years we can hope to get something from them.
President Morris: We can only make a parallel with the pecan. If we know
that it requires fifteen or twenty years for coming into bearing as a
seedling tree, and if we know that it bears frequently in two, three, or
four years after being grafted we can anticipate analogous action with
other species of hickories. I haven't been able to get testimony from
men who have grafted hickories. One man told me he thought shagbark
grafted upon other shagbark, topworked, came into bearing in seven or
eight years. Another man told me that his came into bearing in a much
shorter time than it would otherwise, while with one particular variety,
the Hale, I think that twelve years has been required for the tree to
come into bearing.
Doctor Deming: I have a communication from Mr. Hales in which he speaks
of a tree grafted in 1880, but doesn't say when it began to bear.
Mr. Littlepage: He told me it has taken some of them twenty years.
Doctor Deming: But the pecan on hickory has been known to bear the
second season, that is, topworked. Can we expect such results in
topworking our own hickories?
Mr. Littlepage: I think so.
Doctor Deming: Are we going to have success in topworking, and by what
method?
President Morris: I believe in the South they can graft, but in the
North we have got to do it by budding. My best results have been late
July or early August. I believe herbaceous budding promises a good deal.
Mr. Rush: Were those buds then of the year previous?.
President Morris: Those were buds from the year of the scion, and
herbaceous stock of the year.
Doctor Deming: Mr. Littlepage has had some success in budding hickory
very early, haven't you?
Mr. Littlepage: I was just stating that I started in last year to bud. I
think it would be possible to make a pecan orchard bear early by budding
into these hickories, ten, fifteen, or twenty years old. This next year
I am going to try hickory on hickory. I am going to try three processes.
I am going to try bark grafting, and whip grafting in the body of the
tree which has been cut off. Then, I have quite a number of hickories
each four or five inches in diameter that I have sawed off and allowed
to put up clusters of water sprouts, and I am going to whip graft some
and put paper sacks over them, and see which is the best.
President Morris: I have found budding the best.
Mr. Reed: Doctor Morris referred to the analogy of the pecan grafted on
pecan as coming into bearing in two years. Do you account for that in
the fact of its being a graft, or the fact that the wood you selected
came from a tree that had the characteristic of early bearing?
President Morris: No doubt that characteristic was transmitted, and
further, no doubt the grafted stock was used from bearing wood. Those
points are all of interest.
Mr. Reed: Does the mere operation of grafting or budding influence
earliness of bearing?
President Morris: Yes, if I understand the question rightly. A tree that
might not bear for fifteen years as a seedling may bear in three years
grafted.
Mr. Rush: I have Persian walnuts that bore two fine nuts the second
year. I have young trees, one about thirty inches, and I am sure it
will be full of nuts next year, unless some providential misfortune
should intervene.
Mr. Reed: At what age did the original trees begin to bear?
Mr. Rush: Those were buds shipped to me from California.
Mr. Littlepage: I am firmly convinced that there is something in the
process of budding or grafting that stimulates the growth. For example,
I have scions that were not over four to eight inches long grafted on
one year seedling pecans which, at the end of this season's growth, were
as much as thirty inches high. All along in the same row where seedling
pecans were not grafted, there is none over eighteen inches high.
Mr. Reed: To have made exact comparison, you would have had to take buds
from your seedling nursery trees, and graft on other trees. You are
comparing these buds from one tree with seedlings of another.
Professor Lake: I would like to ask if you didn't bud or graft the best
stocks in the row too?
Mr. Littlepage: We took the whole row, as we came to it, but that
particular tree might have been on some particularly favorable stock. It
is a matter of a good deal of interest to see why a seedling which
wasn't budded at all didn't grow as high as a scion which was budded in
summer, stratified all winter, then put into the ground in an unnatural
position.
Professor Craig: It is the same principle, I think, which we discover in
pruning. If we prune heavily during the dormant season, the effect is
increased vegetative growth. If we wish to stimulate the growth of an
old tree somewhat debilitated, we go to work and cut off a large portion
of the top. We don't disturb the root. The effect is that with the same
amount of pushing power from the root, we have a decreased area over
which that energy is spread, and it results in apparently increased
growth. I am not quite sure if we were to measure it up in a scientific
way, we would actually find it was increased growth. There are fewer
branches, but they have made greater length. In the case of grafting our
pecans, we cut off our tops, set a two-bud scion in the root, and
usually but one starts and receives all the vigor from the established
root, instead of the vigor being distributed over several buds on the
original seedling top. We have as a result of that concentration of
vitality increased growth. I think that theoretical explanation will
stand fairly well, because it seems to be directly in line with the
effect of winter pruning.
Mr. Reed: I would like to ask Professor Craig to what extent he would
select seed for nursery purposes? What influence would the characters of
the parent tree from which the seed came have on the grafted tree?
Professor Craig: I don't believe that we can expect the characters of
our stock to affect the scion to any extent. I think what the nurserymen
should have in mind and keep in mind is a good, vigorous stock, and as
many stocks as possible,--as he can get out of a pound of nuts.
Otherwise, I don't think it cuts much figure. In that connection there
is a principle which I have discovered by experience, namely, that if
you are growing stocks it is wise to get your nuts as near your own
locality as possible. My experience last year in planting five hundred
pounds of northern grown nuts in a southern locality, and five hundred
pounds of southern grown nuts in the same locality, gathered in that
locality, is that I got fifty per cent more trees from my southern grown
nuts than northern, and trees that were fully thirty per cent better.
Mr. Littlepage: Where were your northern grown nuts stratified?
Professor Craig: They were not stratified. They were planted as soon as
they were received, and they were received within two weeks from the
time they were taken from the trees.
Mr. Littlepage: I am inclined to believe that if your northern grown
nuts had been stratified in the North, and undergone the customary
freezing and thawing, then had been taken up in the spring, you wouldn't
have seen that difference.
Professor Craig: I think that point is well taken.
President Morris: There is no doubt about that. In that same
connection--I would choose nuts for seed purposes of a mean type, for
the reason that nature is all the while establishing a mean. The big
pecan is a freak. If you plant big or small nuts, you don't get big or
small nuts in return. You get both big and little seeking a mean.
Mr. Roper: The large nut will give a better tree. We have tested that
out.
President Morris: Does that work out logically in that way, is it a
comparative matter all the time?
Mr. Roper: We haven't worked that out in the bearing, but in the nuts in
the row, the small nuts did not produce as large trees as the large
nuts. We never tested the mean nuts. We did select some of the very
smallest we had, and planted one of the northern and one of the southern
type. They came up, but the trees amounted to nothing.
President Morris: The idea I meant to convey was that both very small
and very large nuts are freaks, and neither likely to give as good a
tree as mean types. What would you anticipate, Professor Craig?
Professor Craig: I think that would resolve itself on a practical basis
from the practical standpoint. I think the mean or average sized nut
would give you the best results. There is no doubt, as Mr. Roper said,
the very small nut would give you weak seedlings. On the other hand, you
couldn't afford to use the very largest, so that a mean between large
and small would be the natural thing to choose. But we should do nothing
to discourage the planting of the finest specimens, with the possibility
of getting something unusually good. That is certainly the work for
every amateur.
Professor Lake: Does that statement, that you think it doesn't make much
difference about the parent of the nuts for stock, apply to walnuts?
Professor Craig: I haven't had any experience in walnuts.
Mr. Littlepage: I would like to ask Mr. Roper if he knows of any
examples where selection of fine varieties of seed has not resulted in
getting a more productive variety of the plant which he was producing?
Mr. Roper: Only one, and that wasn't in a tree.
President Morris: In regard to coming true to type, I think records have
been made of many thousands of pecans, and I don't know of any instance
where the progeny resembled the parent closely.
Mr. Pomeroy: Maybe someone could explain one of my failures a few years
ago in planting some Persian walnuts. I went to another tree in western
New York, and got a peck or more. They were planted the same day, in the
same ground, and all came up. Those I got from another tree resembled a
hill of beans, and stayed that way for three years. Why wouldn't those
grow? In soil three feet from those, there were trees growing. Those
nuts never did make trees. The nuts were of good size.
Colonel Van Duzee: As a practical nurseryman, I wouldn't think of
planting nuts from a tree that I didn't know individually. We have had
very much better success with nursery stock where we have chosen as seed
medium sized nuts from vigorous trees with which we were acquainted. In
the case of Mr. Pomeroy, I don't think there is any question but that
the history of his tree would account for the failure. In other words,
his nursery stock was undoubtedly from the results of years of slow
growth on the part of the original tree, or unfavorable conditions of
some kind. I don't quite agree with Professor Craig on the question of
the influence of stock, because I believe it is really a very important
point.
President Morris: We are not here to agree upon anything.
Colonel Van Duzee: I can't speak from the scientific standpoint, but I
am quite sure that in the nursery business I shouldn't care to overlook
that influence.
President Morris: When men agree, it means we are on stale old ground
which has been thrashed over.
THURSDAY AFTERNOON, DECEMBER 14, 1911.
President Morris: The meeting is called to order. The first paper this
afternoon will be that by Mr. J. Franklin Collins of the United States
Department of Agriculture, on the chestnut bark disease.
THE CHESTNUT BARK DISEASE.
J. FRANKLIN COLLINS, Washington, D. C.
I presume some of you know as much about certain features of this
chestnut disease as I do myself; for I have only worked over certain
sides of the whole question. I also presume that you are all acquainted
with the fact that this disease, which is known as chestnut blight or
the chestnut bark disease, is without doubt the most serious disease of
any forest tree which we have had in this country at any time, that is,
so far as its inroads at present appear to suggest.
I want to call your attention to certain general historical facts in
connection with the disease, facts which are familiar to some of you,
but unfamiliar possibly to others. The Forester of the Bronx Zoological
Park, Dr. Merkel, discovered in the fall of 1904, or had his attention
particularly called in 1904 to the fact, that a good many chestnut trees
were dying in his vicinity, a number sufficient to have attracted
especial attention. He looked at the matter carefully, and decided that
there was a definite disease on these trees. He handed specimens over to
Doctor Murrill of the New York Botanical Garden; who worked out the
disease, and decided that it was a new fungus which was causing the
trouble. He named it _Diaporthe parasitica_, the name under which it is
generally known today, although there is some question as to whether
that is the one which should be applied to it. This, you remember, was
in 1904--in the fall.
The first publication which appeared on the disease was in 1906, as I
recall it. The publication which then appeared was Doctor Murrill's upon
his investigations. The disease has spread very rapidly since then, so
that today we know the disease in a general area indicated by the red
color on this map. The green area indicates in a general way the natural
distribution of the common chestnut. Since 1904 investigations upon the
geographical range of the disease have been carried on so far as to show
that the disease is now known over approximately the area indicated in
red on that map. The northern limits of the disease are perhaps in New
York State. Further east, it is known as far north as northern
Massachusetts, mainly in the western part, and it is also known in
Boston. There have been two or three cases of the disease found in the
Arnold Arboretum. On the west, we have two cases in West Virginia, and
the most southern station which I know of is in Bedford County,
Virginia. But those are isolated stations beyond the area which is
indicated here. I shall have a little more to say in regard to the
distribution.
Before speaking of that, I want to call your attention to a few points
in regard to fungi in general, points of common knowledge to all who
have studied fungi or mycology. A fungus is a kind of plant which does
not, on account of the absence of the green coloring matter, manufacture
its own food. It is a plant which has, in other words, no green foliage,
and as it has no green foliage, it must obtain its organic or elaborated
food from some other source. The fungi have very aptly been termed the
tramps of the vegetable kingdom, that is, they live on food prepared by
somebody else. They can take certain organic substances and change them
apparently into other organic matter which can be used by the plant. In
the case of this chestnut fungus, we have a fairly typical fungus in
certain respects. We have a vegetative stage of the fungus which is
nothing more or less than a lot of threadlike structures penetrating the
bark of the chestnut, the inner bark or the middle bark, and there
drawing the organic matter from the bark of the chestnut and
appropriating it to its own use. Fungi, like practically all other
plants, have two stages of existence, one the vegetative or growing
stage, the other the reproductive stage. Sooner or later the fungus will
produce the fruiting bodies, after it has obtained a sufficient amount
of food to justify the formation of these more highly organized
structures. In the case of the fruiting body of the chestnut fungus, we
have very small, pinhead-like structures, which come out to the surface
of the bark, the vegetative portion developing through the interior of
the bark. On smooth bark we find that these fruiting pustules are apt to
appear all over the surface. With bark that is sufficiently old to have
ridges and crevices, we find these fruiting bodies only in the crevices.
These fruiting pustules which you will see on this bark are the
structures which produce the reproductive bodies, these latter being
known as the spores. There are two types of spores which are produced by
this fungus. One is the type which is commonly spoken of as the summer
spore, the other the type which is spoken of as the winter spore. The
winter spore is known from the point of view of the mycologist as the
perfect stage of the fungus, that is, it is the more characteristic of
this particular fungus. If we should make a cross section of the bark,
we should find that the vegetative stage is running through the middle
bark, and commonly the inner bark, sometimes in one place only,
sometimes in the other only, sometimes in both. This vegetative stage
later sends up in various ways a mass of tissue which results in the
formation of pustules. These appear on the surface, sometimes more or
less regularly rounded, sometimes rather irregular. In the case of the
summer spore stage, we have inside the pustules a mass of tissue which
is formed into spores. The interior of the spore mass, or at least
portions of it, is somewhat mucilaginous, so that when moisture is
applied a swelling of the interior mass is produced at a certain stage
and something has to break. As a result, we have a mucilaginous mass
pressed out through the break in the shape of a twisted thread, much the
same as if you take a collapsible tube of paste and pinch it.
Now, one of those summer spore threads may contain anywhere from one to
five million spores. I have tried to estimate the number in a thread of
this sort which was about an eighth of an inch long, and by taking a
certain portion of that thread, mounting it in a drop of water, and then
counting over a certain measured area under the microscope, I have
estimated, by multiplying, that there were 2,400,000 spores in that one
thread. So you can imagine how many of these spores may be produced by a
single diseased area which has produced perhaps four or five hundred of
those pustules, each pustule containing anywhere from one to twenty
threads. Each one of those spores may develop a new diseased area,
provided it is transported to a fresh break in the bark of a chestnut
tree. Fortunately, only a very small fraction of one per cent ever
reaches the proper place for growth.
This last is what I alluded to as the summer spore stage. There is a
winter spore stage, or technically, the ascospore stage, which comes, as
a rule, later in the development of the fungus. In this same pustule,
later in the season, certain sacs are formed. These have long necks
which extend to the top of the pustule. These sacs are sufficiently
large to be seen with the naked eye. They are dark colored. Inside
these, we have a lot of smaller transparent sacs or cases in each of
which we get eight spores, sometimes in one row, sometimes in two rows.
Each spore can propagate the fungus.
We have, then, two types of spores, either one of which can reproduce
the fungus under suitable conditions. There is still another way by
which the disease may be kept going. The vegetative stage can survive
the winter and continue growing the following year.
I will say right here that I am planning to give you merely an outline
of this disease, and have time afterwards for questions which I think in
a meeting of this sort are one of the most productive sources of
information.